The present invention relates to Wavelength Division Multiplexed (WDM) systems and, more particularly, to the problem of realizing a broadband electronic cross-connect switch using multiwavelength lasers, broadband receivers and wavelength routers.
Wavelength division multiplexing allows high transmission capacity by allowing many wavelengths to be simultaneously transmitted in each fiber. An important device that is then needed at each node is a broadband cross-connect switch providing complete connectivity between incoming and outgoing fibers. Here we assume that all incoming fibers are connected to suitable demultiplexers combined with broadband receivers providing electrical data to the switch. The switch is therefore connected between two sets of data lines, which carry the electrical signals corresponding to the various input and output wavelength channels. Channels must also be added and dropped, and therefore additional lines for these channels must be included. One would like if possible to use to an electronic switch for this purpose. However, for very high bit rates such as 10 Gbit/s, an electronic switch of large size is difficult to realize.
Thus, there is a continuing need for an electronic switch for handling a large number of very high bit rate channels.
In accordance with the present invention, we disclose a programmable broadband cross-connect switch which includes an Nxc3x97N wavelength coupler combined with N tunable lasers, N modulators and N optical receivers. Each of the N tunable lasers can selectively produce N different wavelengths. The coupler couples the N wavelengths to the N modulators. The N modulators modulate the N wavelengths using N input electrical signals, each modulator being selectable by choosing a laser wavelength. The N optical receivers receive and detect the N modulated wavelengths to produce N output electrical signals therefrom, each receiver receiving and detecting a different one of the N different wavelengths. Thus, by selecting a laser wavelength a particular modulator and receiver pair is selected so that a modulated signal, formed at the selected modulator when an input electrical signal modulates the selected wavelength, is switched to the selected receiver. The switch exhibits improved efficiency, simplified lasers, and minimized fiber connections.
According to one aspect of the invention, the programmable broadband cross-connect switch can be arranged as an electronic data cross-bar switch and used to add and/or drop wavelengths from a wavelength division multiplexed signal. According to another aspect, the programmable broadband cross-connect switch can be arranged as a space-wavelength cross-connect which allows connectivity between any wavelength of an input fiber and wavelength of an output fiber.
In accordance with one feature of the invention the Nxc3x97N coupler may be implemented as an Nxc3x97N wavelength router or as a free-space grating. Another feature uses a concentrator for directing the laser signals to the grating. Yet another feature is that the Nxc3x97N coupler and modulator is implemented using a plurality of units and where each coupler unit connects to a subset of the N modulators. A further feature is the use of a selectable laser having Na+Nb controls for producing NaNb wavelengths.